The invention relates to an electric machine for starting an internal combustion engine.
In addition, the invention relates to a method for operating an electric machine for starting an internal combustion engine.
The invention is based on a system having an electric machine such as a starter or a starter motor.
The subject matter of the present invention comprises electric machines, in particular starters for vehicles with internal combustion engines which have an electric machine with a commutator.
Electric machines, in particular starters or generators, having a housing which is sealed, in particular sealed with respect to environmental influences such as the penetration of dirt and/or water, are known from the prior art. These “sealed” starters are used, for example, in mining vehicles or special vehicles. The housing is conventionally sealed by means of various sealing measures such as, for example, by means of O rings.
If a starter is in its position of rest, for example when the starter is not operational, a starter pinion is held in this position of rest by means of spring forces. If the starter is put into operation and in the process the starter heats up, the air in the housing also expands. Owing to the sealing of the housing, this air cannot escape, with the result that an overpressure comes about in the housing. The overpressure gives rise to a force acting on components arranged in the housing, for example on a shaft, in particular an output shaft, which is partially mounted in the housing and presses the output shaft axially forward, that is to say in the direction of a ring gear of the internal combustion engine. As soon as the force acting on the output shaft owing to the overpressure is larger than the spring force acting in the opposite direction, the overpressure causes the pinion mounted on the output shaft to disengage from the ring gear (similarly to a pneumatic piston). Furthermore, the overpressure has the effect that after the starter is switched off the pinion can no longer be moved back into the position of rest since the spring force which is applied for this purpose is lower than the opposing force of the overpressure. The pinion can then abut against the ring gear or after starting cannot be moved, or cannot be moved sufficiently quickly, out of the ring gear into the position of rest. This leads to increased wear at the pinion/ring gear combination up to the point of destruction of the starter if the pinion cannot leave the ring gear. Increasing the spring force of the engagement spring in order to counteract the force of the overpressure would have an adverse effect on the pull-in behavior of the relay.
DE 10 2008 002 272 A1 discloses a housing of a starter with a valve for reducing an overpressure in the housing. However, this valve must be attached to the starter in such a way that it is accessible from the outside, as a result of which said valve is subjected to environmental influences. In the case of applications which are susceptible to dirt, the optimum functioning of the valve over its lifetime is not ensured. Furthermore, starters are often surface coated after their attachment to the internal combustion engine. A surface coating layer can block the valve with the result that its function is adversely affected and the valve can, in particular, no longer open. Furthermore, active control of the valve is necessary for the purpose of opening or closing so as to ensure the targeted reduction in pressure.